Studies on top quark-pair production in pp collisions at the Large Hadron Collider with the ATLAS experiment

The performance of the track based alignment software of the ATLAS Inner Detector was studied. To improve alignment vertex and beam constraints on the track reconstruction were investigated. The b-tagging performance was also investigated. The dependence on the jet reconstruction algorithm, and on the Inner Detector misalignment were studied. A Top quark pair-production cross section measurement with b-tagging was carried out. The systematic uncertainties of less than 30% was estimated.